Incoming SMTP Restrictions Per Domain

Hello, our server is running 11.50 built 19. Things are great, however, we came across an odd issue with one of the domains on the server. We thought we would pose the scenario and see if there are any possible solutions. Example Domain: domain.com E-Maill: mike@domain.com[/EMAIL] Mike recently stated there has been an increase in SPAM messages being delivered to his inbox. We activated a SPAM Protection Service and forwarded all MX records to the SPAM Protection Organization. Mike states, I still get SPAM e-mail. It turns out looking at the source of the e-mail that the incoming e-mail is coming directly to the server and not to the MX record --> SPAM Filter --> back to the server. The SPAM Protection company never sees the bad e-mails to remove them. The SPAM protection company does allow for sending to the domain via dedicated IPs and advised us to implement an inbound SMTP Restriction. How can we accomplish this in WHM / cPanel? We know that domain.com will receive safe / clean messages from inbound smtp servers: 1.1.1.1 2.2.2.2 3.3.3.3 4.4.4.4 How can it be configured that mail for domain.com domain is only accepted from these IPs and the mail from other IPs are ignored? Is this possible. Let me know your thoughts. PS: We want to handle this on a domain level vs a global level as there are some organizations who are not impacted by this problem or who do have SPAM protection service. Thanks for any assistance / guidance on this matter.